Sample Thickness Dependence of Minority Carrier Lifetimes Measured Using an ac Photovoltaic Method

When Si wafer thickness is much smaller than the minority carrier diffusion length, the carrier lifetime, estimated by an ac photovoltaic method previously reported, has been shown to be restricted by the wafer thickness. The thickness dependence of the lifetime was measured on n-type Si wafers with thicknesses from 0.6 to 4 mm. The observed lifetimes ranged from 72.3 µs to 1.1 ms and were in good agreement with those estimated theoretically. It was demonstrated that the bulk lifetime can be obtained with less than a 10% error when the sample thickness is 3.6 times larger than the diffusion length of the minority carriers.